1. Field of Invention
The invention relates generally to an apparatus for the distribution of gas within a process chamber.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is chemical vapor deposition (CVD).
Chemical vapor deposition is generally employed to deposit a thin film on a substrate or semiconductor wafer. Chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on a surface of the substrate that is positioned on a heated substrate support. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
One material frequently formed on substrates using a chemical vapor deposition process is tungsten. A precursor gas that may be used to form tungsten generally includes tungsten hexafluoride (WF6) and silane. As the silane and tungsten hexafluoride mix, some xe2x80x9cstrayxe2x80x9d tungsten (i.e., tungsten that does not deposit on the substrate) condenses and deposits on the showerhead and other chamber components. Generally, tungsten condenses more rapidly on cooler regions of the chamber. This is particularly problematic at the showerhead.
The showerhead is generally situated between the substrate support and the chamber lid. The substrate support may be heated during processing to between about 300 to about 550 degrees Celsius. The lid is typically water-cooled to maintain the lid at about 45 degrees Celsius. The showerhead generally is heated by the substrate support while being cooled by the lid. As the showerhead is in physical contact with the lid, the cooling effect of the lid conducting heat away from the showerhead maintains the showerhead at a temperature near that of the lid. Thus, the low temperature of the showerhead disadvantageously promotes the deposition of unwanted tungsten on the showerhead. Tungsten formed on the showerhead is a potential source of particulate contamination and must be periodically cleaned, generally by etching using a fluorine-based cleaning process. Eventually, the tungsten build-up may clog the holes in the showerhead preventing passage of the precursor gas therethrough. In this condition, the showerhead must be removed and cleaned or replaced.
Therefore, there is a need for a showerhead that minimizes the formation of deposition thereon in a chemical vapor deposition process.
One aspect of the invention generally provides a showerhead for distributing gases in a semiconductor process chamber. In one embodiment, a showerhead comprising a perforated center portion, a mounting portion circumscribing the perforated center portion and a plurality of bosses extending from the mounting portion, each boss having a hole disposed therethrough is provided. Another embodiment of the invention provides a showerhead that includes a mounting portion having a first side circumscribing a perforated center portion. A ring extends from the first side of the mounting portion. A plurality of mounting holes are disposed in the mounting portion radially to either side of the ring.